Glucan polymerization mechanism

In this paper, it has been shown that glucansucrases with different synthetic specificities can synthesize glucans with different structures and can synthesize oligosaccharides with different structures by acceptor reactions. The mechanisms by which these enzymes carry out the polymerization and by which the acceptor reactions occur has been discussed. The products resulting from the... 

Cellulose is present in both primary and secondary cell-walls. However, differences in both the degree of polymerization and the control of chain length between the celluloses from these two sources suggest that the two types of cellulose are formed by different mechanisms.289-291 Whereas the mechanisms responsible for formation and orientation of cellulose fibrils are not yet known, some information is available concerning the enzymes capable of catalyzing the formation of celluloselike, 0-(l—>4)-linked D-glucans (see also, Ref. 217). 

Polymerization of the D-glucan chains occurs by way of a multi-subunit, enzyme complex embedded in the plasma membrane an almost simultaneous association, by means of hydrogen bonds, of the newly formed chains results in formation of partially crystalline microfibrils. This mechanism of polymerization and crystallization results in the creation of microfibrils whose chains are oriented parallel (cellulose I). In A. xylinum, the complex is apparently immobile, but, in cells in which cellulose is deposited as a cell-wall constituent, it seems probable that the force generated by polymerization of the relatively rigid microfibrils propels the complex through the fluid-mosaic membrane. The direction of motion may be guided through the influence of microtubules. 

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